We have to be careful with these types of questions as they to dip quite a bit into the realm of user-created content such as doujinshi and user created music videos.
A Vocaloid characters are typically used with the music composing community for things related and unrelated to anime and manga, amongst them are some notable works such as Bad Apple!!, Just Be Friends, the World is Mine, Black Rock Shooter, Melt, and Rolling Girl, to name just a few. Many of these songs have had remasters, remixes, resamples, or even live/real voice covers. Just because an Vocaloid is identified, it doesn't mean there's a definitive version. There can be different versions of the same song by different Vocaloids form the same of different composers.
While we don't want to discourage question on fan made content, we should limit the scope of these questions to we're not looking for a needle in a haystack. Not all fan made content are created equal. We can't always know what someone else is thinking out and we can't expect them to give us the clues we need to find them. Therefore I propose the following.
Unless we definitively know which Vocaloid performs and at least the composer, and/or artist behind the work (like we as for a series, episode and approximate time for series-based music id-requests), music identification questions do not comply will be marked off-topic.
The ones that give at least include them must give at one of those artifact (image or clip linking the work with it's creator) that connect it to the work they are looking for. Such questions will be tagged with the vocaloid as the "series" and music as the accompanying tag.
Questions not related to music identification, but pertain to Vocaloids, whether that is music or art created using/of them and related fandom will still be considered separate and on-topic.